How to default FORM action and method?

I have written a simple script that takes the contents of any form and sends it via email. However, if it's to be useful in the FCKeditor, the user must know the URL of the script.

I would like to be able to set the default value of the ACTION (txtAction) text box in the form dialogue.
I would also like to be able to default the METHOD (txtMethod) to 'POST' rather than 'GET'

I have had a hunt around the fck_form.html file, but changes here are not effective.

Is there a config setting for this or should I be using the Javascript API? Any help appreciated.